1. Technical Field
The present invention generally relates to a device for measuring dissolved air in a fluid or process mixture flowing in a process line.
2. Description of Related Art
Monitoring levels of entrained and dissolved gases is desirable in many industrial processes. For example, entrained and dissolved gases in the approach system of paper making machines are often problematic, leading to a wide variety of problems, including flow line pulsations, pin-holes in the produced paper, reduced paper sheet strength, and excessive build-up of aerobic growths.
Entrained gases are gases that exist in a gaseous form, mixed in the process fluid. For many industrial applications with small, less than ±20% gas fraction by volume, the gas is typically in the form of small bubbles contained in a liquid continuous mixture. Entrained gases exist as either free bubbles moving within the stock or as bound (or residual) air that is adhered to the fiber. In either cases, entrained air can generally be detected by monitoring the compressibility of the mixture and correlating the compressibility to volumetric percentage of entrained air.
Dissolved gases are dissolved within the mixture on a molecular level. While in the solution, dissolved gases pose few operation problems. Typically dissolved gases have a negligible effect on the compressibility of the mixture. Thus, dissolved gases are difficult to detect via compressibility measurements.
Although dissolved gases are typically not problematic while dissolved, problems arise when dissolved gases come out of a solution as a result of either decreases in pressure or increases in temperature. One example of this is in pressurized head boxes on paper machines where the pressure drop associated with spraying the pulp/water mixture on to the paper machine can cause dissolved gases to come out of the solution and form entrained air.
Thus, to accurately monitor problems associated with entrained and dissolve gases, it is desirable to be able to measure both quantities.